Many fabricators of welded metal products use the open root butt joint as a means to join two pieces of metal together. Fabricators are often forced to weld joints from one side when access to both sides is undesirable or at times even impossible. Furthermore, open root joints are generally employed when the use of joint backer materials is not possible.
Within the butt weld, the first pass, or root pass is often the most difficult to make and yet is also the most critical weld of the joint because the weld bead produced by this first pass serves as the bead face on the back side of the weld. The root pass is considered difficult because it has the least access, being the furthest back at the bottom of the joint. Also, it is made upon an open root, without any support from a metal backing from the parent metal or previous weld. The only support of the weld comes from the thin beveled ends on either side of the joint. An open root weld is considered the most critical because the repair of defects can generally not be made from the back side of the weld. In many implementations of welded structures, if even small defects exist in the root bead, premature failure of the weld may result.
Numerous fabricators successfully weld open root butt joints from one side. Applications include pipe welding in the field and fabrication shop, welding structural shapes and plates where access to the back side is not possible. As expected, the root pass of the open root weld must be welded at somewhat slower procedures than other subsequent passes. This ensures the proper workmanship is maintained and the desired weld quality is obtained. Many of these welds are made out of positions requiring even slower procedures to obtain the desired results. Often a production bottleneck occurs around the completion of this root pass of open root welds.
Accordingly, there is a need for an electrode and welding method that produces a high quality root bead of a single sided butt joint, in a relatively simple and time effective manner.